Washington: The number of Republican voters who do not believe in evolution has jumped from 43 per cent to 54 per cent in the past four years, research has found.

The survey on religious views by the Pew Research Centre found that over the same period the number of Democrats believing in evolution climbed from 64 per cent to 67 per cent.

Just 60 per cent of Americans agreed that ‘‘humans and other living things have evolved over time’’; 33per cent rejected the notion, a number barely changed since 2009, when Pew last conducted this research.

The researchers reported that this partisan difference remained even when the racial and ethnic differences in party make-up were accounted for.

Larry Sabato, professor of politics at the University of Virginia, said the high level of belief in creationism and its rapid rise in Republican ranks shocked him.

‘‘I knew it was bad, but I didn’t know it was this bad,’’ he said.

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According to Dr Sabato, who is a leading American political analyst, the increase in the number of Republicans believing in creationism is a product of the continuing polarisation of politics in America.

As the Republican Party shifts further to the right, social moderates are abandoning it. He also believes the Tea Party movement that rose at the 2010 midterm election has contributed to the increase.

And he believes that religious fundamentalism within the Republican Party is self-sustaining.

‘‘The more people who identify as religious are vocal in the party, the less likely you are going to have groups [within it] who accept the 20th century, let alone the 21st century.’’

He said elements of the party base have veered so far to the right that America finds itself with a ‘‘one-and-a-half-party system rather than a two-party system’’.

In his view this means that the Republican Party will remain competitive during midterm elections, when people typically turn out to vote against whoever holds the White House, but it will find it harder to win the presidency during competitive races.

‘‘If you talk to the leadership off-record they are really worried about this,’’ he said.

Mike Lofgren worked for the Republicans on Capitol Hill for 28 years before quitting in 2011 and publishing the essay that made him famous, ‘‘Goodbye to All That: Reflections of a GOP Operative Who Left the Cult’’.

He said Pew’s findings did not surprise him but did disturb him. According to Lofgren the religious right in America began ‘‘infiltrating’’ the Republican Party a generation ago, beginning at a grassroots level by winning control of things like school boards.

Party strategists saw a new constituency and began to ‘‘pander to them’’, Mr Lofgren said. ‘‘Now the tail is wagging the dog.’’

He says that the Obama administration is not being subjected to proper scrutiny because elements of the far right are focusing on non-issues, such as the President’s nationality or false reports of ‘‘death panels’’ in the Affordable Care Act.

This means that not only are Republicans wasting their energies, they are engendering sympathy for the President among centrists who might otherwise be more critical of him, Mr Lofgren says.

‘‘It is troubling to me because I would like to see two viable competitive parties with alternative views, but alternative views that are grounded in sanity.

He said since he quit the party he has seen other friends and former colleagues follow suit, some of them speaking openly and derisively about the religious right.

Dr Sabato says the Republican leadership is hoping that the party’s next presidential nominee is a ‘‘Chris Christie figure’’, meaning a person with centrist social views, rather than one of the party’s prominent figures of the religious right, such as Rick Santorum.

But he says the party’s base may well select a figure of the far right. ‘‘Sometimes a party learns after it has been hit over the head a couple times with a two-by-four; sometimes it takes five or six times.’’

He says the religious right within the Republican Party not only alienates young people, women and gays, it fails to attract other key religious demographics who tend to vote on economic issues rather than social issues, such as African Americans and Hispanics.

Pew conducted interviews with 1983 adults across America and reports a 3 per cent margin of error.